1. Field of the Invention
The present invention relates to an improved radial shaft seal, more particularly, to an oil-tight seal between two mechanical parts which are assembled coaxially and rotatively relative to each other. The invention is especially suited to be used for sealing between a stationary shaft and the bore of a rotating wheel hub.
2. Description of the Prior Art
A unitized shaft seal for sealing between a stationary shaft and the bore of a rotating housing as shown in FIG. 4 is known from U.S. Pat. No. 3,561,770. Referring to FIG. 4, unitized seal 100 comprises: rotary wear sleeve assembly 101 which has a hole 102 and is mounted in a rotary housing (not shown); and a stationary seal element 104 mounted on a stationary shaft (not shown). The stationary seal element 104 is provided with a seal lip 105 and a spring 107 disposed in the seal lip 105 which urges the seal lip 105 on a peripheral outer cylindrical surface inside the bent portion 106. A dirt exclusion lip 108 is provided at the axial end of the inside cylindrical portion of the stationary seal element 104 to exclude dirt from getting inside the seal.
In the prior art unitized seal 100 constructed as described above, the stationary seal lip 105 slides in contacting engagement against the rotary wear sleeve 101 which is mounted on the rotary housing and the dirt exclusion lip 108 also slides in contacting engagement with the rotary wear sleeve 101, and thus the lip 105 seals inside oil from leaking outwardly and the lip 108 excludes outside dirt contaminants from getting inside.
However, this prior art unitized seal 100 has disadvantages such as the peripheral outer cylindrical surface, on which the seal lip 105 slides, must be finished precisely, and at the same time, the seal lip 105 must have a precise and smooth inside lip surface as the lip 105 works radially and seals the inside oil by a pumping action generated between sliding surfaces as a result of axial contact load distribution of the lip, and/or a hydrodynamic action of helical or bidirectional inclined, or regmented ridges provided on the sealing surface.
Furthermore, the unitized seal 100 has a deficiency of a shortened usable life owing to significant wear of the sealing lip 105 and the sliding surface of the rotary wear sleeve 101 by the effect of the total radial contact load of the sealing lip 105 which is constructed of continuous annular rubber and a spring enclosed in the sealing lip 105.
Adding to the above, the cost of the unitized seal is expensive because the construction of the parts are complicated and more time is necessary to manufacture it.